1. Field of the Invention
The present invention relates to an electrode device for intracardiac stimulation of heart tissue and/or sensing heart signals in a patient, of the type having an electrode cable containing at least two elongate, flexible conductors, insulated from each other, and with an electrode head, arranged at the distal end of the electrode cable and provided with at least two conductive surfaces, each connected to a separate conductor.
2. Description of the Prior Art
An electrode device of the above general type is disclosed in U.S. Pat. No. 5,306,292. In one embodiment, the electrode head of this known electrode device is equipped with a number of punctiform conductive surfaces. In a second embodiment, the electrode head is formed by two conductive bodies, one of the bodies being a centrally arranged projecting part which is insulated from the other conductive body. In another embodiment disclosed in this patent, one of the conductive surfaces is arranged on the end of the electrode cable, and the second conductive surface is formed by part of a traumatic, helical fixing means on the electrode head.
U.S. Pat. No. 4,848,352 describes another pacemaker electrode of the type initially described, with a head subdivided into sections of conductive material insulated from each other.
The conductive surfaces in these known electrode devices serve as stimulation surfaces and as sensing surfaces. In some of the embodiments of these known electrode devices, the distance between the stimulation surfaces and, accordingly, even the distances between a stimulation surface and a sensing surface, can be varied when different conductive surfaces are connected by a pacemaker having a switching stage. The distance between stimulation surfaces is governed to a large degree by the system's impedance, i.e. the larger the distance between stimulation surfaces, the larger the impedance obtained. This means that the physician might wish to reduce the distance between stimulation surfaces, if e.g. the threshold value is too high, so current increases and voltage decreases. In the prior art electrode devices cited herein, the change in distance between stimulation surfaces on the head of the electrode device is very limited, since the electrode cable can only hold a limited number of conductors, thereby limiting the number of conductive surfaces on the electrode head. Moreover, the change in distance is predetermined, since the conductive surfaces are permanently arranged on the electrode head with a fixed distance between them.